1. Field of the Invention
This invention relates to a block copolymer identified as poly(propylene fumarate -co- ethylene oxide), to a method of synthesizing this block copolymer and to a method of using it.
2. Description of the Prior Art
Polymers have found significant utility in the modem world. Whenever there is a particular need for a material having a specific property or set of properties, scientists often look to polymers to meet that need. In the field of medicine, for example, there is a continuing need for polymers that meet very specific requirements. Some of the properties of a polymer that may be important in biomedical applications, include biocompatability, mechanical strength, consistency, plasticity, resiliency, permeability, crosslinking ability and biodegradability.
One polymer that has been successfully used in the field of medicine is poly(propylene fumarate) (PPF). U.S. Pat. No. 4,888,413, issued to Domb, describes some of the medical uses for PPF and various methods of synthesizing it. Also, PPF has been described in Biopolymeric Controlled Release Systems Volume II, Donald L. Wise, et al., Chapter 11, 170-184, and in "The Formation of Propylene Fumarate Oligomers for Use in Bioerodible Bone Cement Composites," by A. J. Domb, et al., JournaI of Polymer Science: Part A: Polymer Chemistry, Vol 28, 973-985 (1990). Generally, poly(propylene fumarate) is useful as a bone cement became it crosslinks to form a solid having appropriate compressive strength.
Another polymer that has been used in other applications in the medical field is poly(ethylene oxide) (PEO) which has the chemical composition, HO--[--CH.sub.2 --CH.sub.2 --O--].sub.m --H. This compound is also called poly(ethylene glycol) (PEG) when the molecular weight is less than about 20,000. In this description, the term "PEO" will be used generally to describe the chemical composition, HO--[--CH.sub.2 --CH.sub.2 --O--].sub.m --H, without regard to the molecular weight. Some of the medical applications of PEO are discussed in Poly(Ethylene Glycol) Chemistry: Biotechnical and Biomedical Applications, edited by J. M. Harris, 1992.
PEO has also been used in the medical field as a copolymer. For example, "Bioerodible Hydrogels Based on Photopolymerized Poly(ethylene glycol)-co-poly(.alpha.-hydroxy acid) Diacrylate Macromers," Macromolecules, A. S. Sawhney, et al., vol 26, 581-587, describes a copolymer that functions as a biodegradable hydrogel for delivering drugs.
However, these polymers and copolymers are not suitable in some specialized applications. For example, it would be desirable to have a biodegradable polymer that is crosslinkable at body temperature, i.e., about 37.degree. C. Such a polymer would have special utility as a material for vascular implants. Instead of inserting a solid vascular implant which has the potential of damaging the walls of an artery during implantation, the surgeon could simply inject through a catheter a fluid polymer which could be crosslinked in situ to form a vascular implant. Such a material would permit the implantation of a vascular implant without unduly traumatizing the walls of the artery.